This page lists successful half treed saddles, and those with flexible trees, etc...
Part and alternative treed saddles are not a magic pill. They do require a certain amount of fitting and the fit needs checking as per a regular treed saddle. They saddles can cause as much damage as a treed saddle to your horse if you get the padding wrong or use the saddle in a way not recommended by the manufacturers. My best advice to you is to get a representative or agent from the company whose saddle you're looking to buy out to assess you and your horse and to advise on padding and suitability. Don't just settle for the first one you try or the cheapest and listen to your horse.
The Fhoenix FA is the new saddle from Heather Moffett. Not available to the US, but available in many different styles and models. This saddle is unique in that the half tree is at the back of the saddle.
The Balance Soft Option is more of a traditional half tree saddle although it has had good reviews. No longer in production, but there are plenty of them about, and you should be able to pick one up secondhand.
The MacKinder Flex Tree saddle has a foam tree and is successfully being used for Endurance riding.
The Trapezius saddle has flexible panels and is designed so as to not impede the horse's movement.
The Floki Icelandic saddle has a soft PVC tree however is not recommended for undermuscled horses.
The Reactor Panel saddles has flexible panels that move with the horse. They also have shortened tree points to allow the shoulder freedom to move.
Similar to the Reactor Panel is the Free 'n' Easy.
The WOW Saddle is a patented design of saddle that can be tailored to horse and rider by interchanging headplates, seats, flaps and panels. It is fitted with Flair and is completely adjustable.
Orthoflex saddles have flexible panels that move with the horse.
The HooBee saddle is still in the testing stage and due for pressure testing in the near future. It has a section of tree at the front of the saddle, to which the stirrups attach. The rest of the saddle is soft and mouldable.
Specialized Saddles have a patented system that
allows you to independently adjust all three dimensions of saddle fit:
width, arch and angle.The saddles come in 5 styles and have 3 choices of stirrup positioning.